1. Field of the Invention
This invention relates to an angle-adjusting apparatus, and more particularly, to an angle-adjusting apparatus for a reflection mirror in a rear-projection TV.
2. Description of Related Art
Rear-projection televisions are generally used for the purposes of displaying education programs and simulation training programs such as piloting an airplane or driving a car. As the quality of life and the standard of living improve, rear-projection color TVs become desirable appliances to consumers.
A rear-projection TV uses a projection apparatus located behind the screen and a reflection mirror to reflect the light from the projection apparatus and to form an image on the screen. Compared with a conventional TV of cathode ray tube (CRT) type, a rear-projection TV has the advantages of no radiation, large screen size, and connectivity to a computer or other video equipment for educational or entertainment purposes. It is believed that the rear-projection TV will play an essential role in the entertainment display market, and therefore. Manufacturers of rear-projection TVs have made efforts to improve the image qualities, such as color intensity, focusing clarity, image resolution, and contrast.
The reflection mirror is an essential component in the rear-projection TV. The reflection mirror must reflect the light emitted from the light projector at a proper reflection angle, so that the desired image is precisely projected onto the screen. A good angle-adjusting apparatus for the reflection mirror can improve the focusing clarity and the image resolution of the rear-projection television type. The conventional angle-adjusting apparatus is shown in FIG. 1A and FIG. 1B. The rotatable base plate 104 is attached to the holding base 102 by the adjusting screws 112a, 112b, 112c, and 112d. A soft grommet 110 is implemented between the rotatable base plate 104 and an affixing screw 106. The reflection mirror 108 is situated on the rotatable base plate 104, and has an X-axis and a Y-axis perpendicular to each other. As shown in FIG. 1A, the X-axis points in a direction perpendicular to the plane of the drawing sheet, and the Y-axis points in a direction parallel to the drawing sheet, wherein the point of intersection is above the soft grommet 110. Adjusting the angle of the reflection mirror 108 is achieved by adjusting the angles of the X-axis and the Y-axis. The reflection mirror 108 can be adjusted to rotate along the X-axis by simultaneously operating the adjusting screws 112a and 112b. Similarly, the reflection mirror 108 can be adjusted to rotate along the Y-axis by simultaneously operating the adjusting screws 112c and 112d. In addition, while the reflection mirror 108 is rotating, the center of rotation remains located within the soft grommet, but its exact location shifts slightly.
When one uses the conventional angle-adjusting apparatus to adjust the reflection mirror, it is inevitable to encounter the following drawbacks:
1. In the ideal situation, the reflection mirror rotates along the X-axis or the Y-axis when the angle adjustment of the reflection mirror 108 is performed. However, in practice, the rotation center of the reflection mirror 108 shifts within the soft grommet 110 during the angle-adjustment procedure. The rotation center is not fixed because the shape of the soft grommet 110 deforms according to the adjustments in the four adjusting screws. Thus, it becomes very difficult and time consuming to adjust the angle about the X-axis and the angle about the Y-axis. For example, if the user has adjusted for the proper angle along the X-axis and then starts to adjust the angle along the Y-axis, the adjusted angle along the X-axis would be changed due to the shift in the rotation center. Therefore, the user must adjust the angle along the X-axis again. However, the angle along the Y-axis is changed while adjusting the angle along the X-axis. As a result, the user has to repeatedly adjust the angles along the X-axis and the Y-axis separately before the proper angles can be properly set.
2. It is easy to cause distortion and deformation of the reflection mirror if the user has insufficient skill to correctly adjust the angle of the mirror. When the user adjusts the angle along the Y-axis, the user has to rotate both adjusting screws 112a and 112b. For example, the adjusting screw 112a is turned in and the adjusting screw 112b is turned out simultaneously. In addition, the user must have sufficient skill to make the adjustment properly because the amount of adjustment for the adjusting screw 112a must be equal the amount of adjustment for the adjusting screw 112b. Otherwise, the reflection mirror 108 would be distorted or deformed. If the reflection mirror is distorted or deformed, it will cause the misalignment of the image pixel, resulting in a deformed image and poor resolution. This problem can severely affect the image quality of the rear-projection TV type. In addition, the conventional angle-adjustment apparatus, as shown in FIG. 1, is difficult to operate, and thus, making micro adjustments becomes even more difficult. This is inconvenient to the user.